Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$142.74	8.736%	$155.2098	$155.21	$155.20	$155.20
Purchase #2	$246.45	3.639%	$255.4183	$255.42	$255.40	$255.40
Purchase #3	$154.59	5.342%	$162.8482	$162.85	$162.85	$162.80
Purchase #4	$106.42	5.166%	$111.9177	$111.92	$111.90	$111.90
Purchase #5	$123.69	10.142%	$136.2346	$136.23	$136.25	$136.20
Purchase #6	$89.72	5.392%	$94.5577	$94.56	$94.55	$94.60
Purchase #7	$16.62	11.585%	$18.5454	$18.55	$18.55	$18.50
7 purchase totals =	$880.23		$934.7317	$934.74	$934.70	$934.60